The present invention relates to a brushless generator, and more particularly to a rectifier carried by a rotor thereof.
Full wave, three phase rectifiers are employed in a variety of environments. Depending upon the specific environment in which they are used, various requirements attend the construction of the rectifier. One application requiring somewhat unusual constraints upon the rectifier design is in so-called “brushless generators.”
A typical brushless generator has three distinct generating systems, including a main generator, an exciter and a permanent magnet generator. The permanent magnet generator includes permanent magnets for establishing a magnetic field which is employed to induce current in a set of windings. This induced current is in turn employed to generate a magnetic field in the exciter; and this magnetic field in turn is employed to induce an even higher level of current, typically three phase alternating, which is then employed to generate a magnetic field for the main generator.
In a typical brushless generator construction, three phase windings forming part of the exciter are carried by the rotor. Rotor rotation results in the generation, in such windings, of a three phase signal. Such signal is then rectified to provide a source of direct current to the main field winding of the generator which is also carried by the rotor.
In many generating systems, particularly those that operate at high speeds, it is highly desirable to eliminate the brushes since they frequently require maintenance or replacement. Moreover, by their very nature, brushes may introduce transients into the electrical energy being outputted which in turn may interfere with the proper operation of some types of electrical loads being driven thereby.
A typical approach used to eliminate brushes in a generator design requires locating the magnetic field of the main generator on the rotor. Electric power is generated in the main stator and can be supplied to external loads using simple electrical conductors. With this approach, the main rotor winding must be supplied with direct current in order to generate a suitable magnetic field. Since the output of the exciter is an alternating current, this current must be rectified to direct current such that it is accordingly necessary that the rectifier interconnecting the exciter and the main generator field winding be carried by the rotor of the generator.
As the rectifier assembly is carried by the rotating shaft of the generating system, the diodes within the rectifier assembly are located in a relatively harsh environment. This environment includes: mechanical/vibration loads, hydraulic fluid flow, and temperature extremes. The harsh environment is in addition to potential handling damage of the diodes during assembly and maintenance.
Mechanical loading of the diode occurs through several factors. High centrifugal forces are generated due to the rotational speed which increase as a square of the speed. Mechanical loads also occur through differential thermal growth between the housing structure material and electrical connection material. These loads are present and cyclic over the life of the unit.
It will also be appreciated that it is highly desirable to minimize the space occupied by the rectifier assembly in order to reduce the overall size and weight of a generator. Still another desirable feature is the provision for cooling of the rectifier assembly during operation since cooling not only minimizes the possibility of thermal damage to the components, but also provides a greater capacity over a correspondingly sized, uncooled rectifier assembly.
Various conventional rotating rectifier designs locate the rectifier within the main rotor shaft to optimize packaging and electrical connections. However, increased power electromagnetic designs or packaging constraints may prevent location of the diode assembly within the shaft due to size and electrical connection limitations.
Accordingly, it is desirable to provide a compact three phase, full wave rotating rectifier assembly which mounts about the rotor shaft and meets the above stated requisites for operation within a relatively harsh environment.